To address a continuous increase of communication service requirements, a common practice adopted by operators to deliver new services to subscribers, or to upgrade a prior network and improve subscribers combination, based on a already laid subscriber line network, is: to move broadband or narrowband devices nearer to a subscriber side, and utilize subscriber lines, such as twisted pairs or coaxial cables, as the uplink channel. This practice allows more subscribers and more services at the subscriber side.
When more broadband and narrowband devices are moved to the subscriber side, a supply of power for remote devices becomes a problem uneasy to be solved, because, at the subscriber side, the environment is complex, and it is inconvenient to supply power in most situations.
A method of line powering, in which an office end provides power for remote devices via subscriber lines, has grown into a major technical solution for operators to acquire subscribers and expand services. After adoption of a line powering technology, a power supply for remote devices is largely enhanced in reliability and maintainability. The technology is applied to more and more network products.
FIG. 1 illustrates an operating principle of a system for line powering in related arts.
As shown in FIG. 1, a power provided by an office-end Power Supply Unit (PSU) may be directly transmitted over subscriber lines or coupled to and transmitted over subscriber lines to a remote device. When the power is directly transmitted over subscriber lines, the remote device receives the power directly. When the power is coupled to and transmitted over subscriber lines, a decoupling unit is needed at the remote device to decouple signal and power.
To enhance the reliability of line powering, power supply redundancy is usually used. FIG. 2 shows a principle of implementing a system for line powering in related arts with power supply redundancy.
In FIG. 2, the office-end PSU is usually in the form of a separate device or a module in a device. Each pair of subscriber lines connected to the office-end PSU has a rectifier/boost circuit to enable the boost of power. A boosted power takes up some pairs of subscriber lines directly and is transmitted over the subscriber lines in a separate manner. Likewise, in the remote device, a step-down circuit is set corresponding to each of the pairs of subscriber lines to reduce the power voltage. The power, with voltage reduced, is combined inside the PSU at a remote end.
In the related system, the office-end PSU provides separate power to each pair of subscriber lines. Every pair of subscriber lines backs up one another. This system, therefore, can be called a line powering system with subscriber line backup.
The transformers, diodes and Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) shown in FIG. 2 and the circuits they form are for illustration of regulating voltage circuits, such as the boost circuits or step-down circuits. They do not represent the specific structure and circuit features inside the office-end PSU and the remote device.
In the related system with subscriber line backup, the office-end PSU provides separate power to each pair of subscriber lines. A rectifier/boost circuit is set inside the office-end PSU and a step-down circuit is set inside the remote device for each of the pairs of subscriber lines. This increases the cost of the line powering system. When more remote devices are added, this cost will be even higher.